As large scale integrated circuits based on silicon are being developed, there are problems with a decrease in the electric properties of DRAM (dynamic random access memory). In particular, the effective thickness of a SiO2 layer used as a capacitor thin film of DRAM gradually decreases due to the large scale integration, resulting in a leakage current caused by electron tunneling. To solve these problems, a method has been developed for improving integrated circuit reliability by etching trenches into the silicon of a semiconductor substrate, and thereby, increasing the effective surface area thereof. However, the above method is facing limitations in terms of the diversification of the final product image. As for other methods, there is a method of increasing the dielectric constant of a dielectric thin film. The larger the dielectric constant of a dielectric thin film is, the thicker the effective thickness thereof can be; thus, a great deal of research is being conducted on the above method.
In particular, in order to develop new materials for a dielectric thin film having a high dielectric constant sufficient for replacing SiO2 (∈r≈4), a number of studies have been conducted on materials having an intermediate dielectric constant such as amorphous Si—O—N (∈r≈6), amorphous or crystalline Ta2O5 (∈r≈23), Zr—Sn—Ti—O (∈r≈50) and the like, as well as those having a high dielectric constant such as (Ba,Sr)TiO3 (BSTO, ∈r≈200). BSTO is being regarded as a potential candidate for the next-generation dielectric thin film for G-bit scale DRAMs due to its high dielectric constant, low temperature coefficient, excellent compatibility with silicon devices, and the like. However, in the field of silicon devices, there has been a reluctance to use BSTO as an alternative dielectric thin film because BSTO exhibits non-linear dielectric properties (ΔC/C0) and high dielectric loss. Such non-linear dielectric properties (i.e., tunability) are suitable for tunable devices such as tunable filters, but severely affects the operation of DRAM devices. Further, in order to utilize BSTO as a DRAM device, its dielectric loss must be lower than 0.005. However, the dielectric loss of the currently available BSTO thin films is only 0.02. It has been reported that the dielectric loss of the BSTO thin film can be reduced by up to 0.01 by regulating various physical properties, including texturing, interface, stress, surface roughness and microstructure of the thin film, but there is still a need to reduce the above dielectric loss by half.
Memory integrated circuits based on semi-conductors such as DRAM require a capacitor layer for storing electric charges and can be utilized as a memory device by utilizing the electrically charged/uncharged states of the above capacitor layer. The capacitance value of the capacitor layer is proportional to the surface area and dielectric constant thereof while being inversely proportional to the thickness thereof. Therefore, in case of using dielectric substances having the same dielectric constant in the large scale integration of a semi-conductor device, the surface area of the capacitor layer is reduced. Thus, in order to achieve the desired level of capacitance, the thickness of the dielectric thin film must be reduced. Currently, as the integration efficiencies of semi-conductor devices improve, methods of reducing the thickness of a dielectric thin film (mainly, SiO2) are mostly used, but such methods will soon reach limits in the field of next-generation G-bit scale DRAMs, and finally, face problems in terms of large leakage currents.
The present inventors have therefore carried out research to solve the above problems with the conventional methods and found that, when SnO2 is added to a BSTO dielectric thin film by a continuous diffusion gradient manner in composition, non-linear dielectric properties of BSTO are converted into linear dielectric properties. The thus obtained linear dielectric thin film composition has several advantages in that: there is little change in the capacitance according to the applied electric field; it has a high dielectric constant capable of showing a desired capacitance even at a thickness suitable for preventing the occurrence of electron tunneling; and it exhibits paraelectric properties similar to the conventional dielectric substances such as SiO2 while having a very low dielectric loss.